A number of proposals have previously been made for improving the surface physical characteristics of leather-like sheet materials having a porous surface layer made of a polymer mainly comprising polyurethane. A principal objective has been to reproduce as nearly as possible the texture, performance and visual characteristics of natural leather. In particular, attempts have been made to improve the shape and appearance of surface wrinkles and creases, air permeability, moisture permeability, resiliency, and so on by modifying raw materials, manufacturing conditions and or other factors to thereby modify the structure and constitution of the leather-like sheet material in question.
For example, Japanese Patent Publication Nos. 20273/65, 38623/72 and 963/79 disclose removing the skin layer of a sheet material by abrading the porous surface having a honeycomb-like porous structure (average diameter about 20-200 .mu.m) and forming a polymer coat layer on the thus-exposed surface in order to improve the characteristics of the material. Most of the pores thus formed are not less than 10 .mu.m in size, thereby converting the surface to the so-called grain side. Japanese Patent Publication Nos. 10345/81 and 10346/81 disclose leather-like sheet materials having microholes on the surface, which are produced by coating a porous surface layer having a large number of microholes, 3-100 .mu.m in size, with a polyurethane solution to thereby adjust the size of the microholes. Japanese Patent Publication No. 47522/86 discloses a method of finishing leather-like sheet materials which comprises applying a dispersion of fine particles of a polymer, for example polyurethane, to a surface having microholes. Japanese Patent Publication No. 44111/80 proposes to use a composition in which a methacrylic ester polymer is dispersed in a polyurethane solution as a finish coating composition. Japanese Patent Publication No. 42109/84 proposes to apply a polycyclic carboxylic acid containing at least 11 carbon atoms or an ester thereof to obtain an improvement in the feeling and texture of the surface.
While these efforts have achieved some improvements in appearance and performance characteristics of leather-like sheet materials, for example by rendering them similar in shape of wrinkles and creases to natural leathers, improving the drapability, or increasing the air permeability and moisture permeability, the prior art leather-like sheet materials are still dry and feel rough to the touch. It has therefore been necessary to treat the prior art leather-like sheet materials with a softening agent, plasticizer or an oil to obtain a natural feeling leather-like material which is soft and also moist to the touch. However, use of such treating agents is not particularly desirable, since the use of such agents alone often leads to stickiness or to bleeding of the treating agent upon lapse of time or unfavorable influences of said agent on the polyurethane. The stickiness or bleeding property of the treating agent is, of course, a function of the particular agent employed.